This project consists of anatomical and physiological studies of the properties and functions of norepinephrine-containing neurons in the squirrel monkey brain. Specifically, we have used histochemical neuronal pathway tracing techniques to demonstrate that there is a projection from locus coeruleus to many areas of neocortex in this primate brain. Further, we have utilized the technique of microiontophoresis in awake animals to determine that neurons in auditory neocortex decrease their spontaneous and stimulus evoked discharge rates in response to local application of norepinephrine. We are currently using metal microelectrodes to record the discharge activity of locus coeruleus neurons during sensory stimulation and operant responding.